Process of producing metals for electrical purposes



Patented Jan. 5, 1937 1 PROCESS OF PRODUCING METALS FOR ELECTRICAL PURPOSES I 7 Anton Wimmer, Dortmund, Germany N Drawing. Application June' 20, 1934, Serial No. 731,575. In Germany November 19, 1932 4 Claims. (01.143-12) Thus I have found that in order to obtain good results the perc'entageof thickness-reduction in. each of the cold-rolling passes except the last should be much less than customary hitherto, and should be chosen according to the silicon My present invention relates to the production of metals having desirable electrical properties, such as a low watt-loss; high magnetic induction (magnetic flux density), and high maximum 5 permeability. Such metals are produced, for instance, in the form of sheets, strips or wires to be used'in the construction of dynamos or transformers, but I desire it to be understood that various other articles'may be made from the improved material produced according to my inven-' tion. 1

The metal employed hitherto is iron or steel,

- generally containing a certain proportion orsilicon, sayup to about 5%. This material is re- 16 duced to the desired final thickness in a series of stages by successive deforming or thickness-re- Q ducing operations such as rolling (in the case of sheets or strips) or drawing (in the case of wires). Between successive thickness-reducing 20 operations or passes) which according to previous practice. may be performed hot or cold, that is,

wlth'or without the simultaneous application of heat) the material has sometimes been subjected to intermediate heating. In the practiceprevail- 1 2:; ing prior to my present invention, the aim has generally been to employ as few passes as pos-,

sible, which means that at each pass the reduction in thickness was carried as far as possible,

even above 50%, within the limits set by the increase in the strength of the material.

My improved process is conducted under spe-' cial conditions having for their'purpose to secure a very considerable increase in the size of the grains or particles of the finished product. 35. The electrical properties of the product are greatly improved as the size of the grains or particles increases. With my invention I obtain readily grains having a. size of square centimeter and more, even to 10 square centimeters 40 and over, which is beyond anything accomplished hitherto, and the enhancement of valuable electrical properties corresponds to this unprecedentedgrowth in the size of the grains.

I have found that it is by no means immaterial in what sequence the several colderolling thickness-reducing steps or passes (with intervening heat treatments) are performed and what to obtain much better results than hitherto, par- 1 ticularly-as' to securing a considerable increase in magnetic induction (m'agnetic' flu}; density) simultaneously .with a reduction of the watt- 66 losses.

ice

content, being smaller as such content increases.

In these passes, which I may term preliminary or main passes, the thickness-reducing percentage should be from about 35' to 5% according as the silicon content varies from 0.5 to 5%. In the final cold-rolling pass, however, the thicknessreducing percentage should be what is known as the critical percentage, which again depends on the particular proportion of silicon, and generally speaking lies about'between 0.5 and 15%, being 1 indicated more specifically in the following table:

Silicon content Critical roentsge of t cknessreduction 1 Permit o. 5 1 2 B 3. 5 4. 5 and over In each of the preliminary passes, the percentage of thickness-reductionshould be greater than the critical percentageffor the particular silicon content. For instance, if the silicon content is 2% (in which case the critical thicknessreducing percentage is from 3 to 8%, as stated above), the percentage of thickness-reduction for each of the preliminary passes would be, say, 33%. With a higher silicon content (with which the critical percentage of thickness-reduction is quite low), the percentage of thickness-reduction during each of the preliminary passes would likewise be lowered, but would in each case still be higher than the critical percentage corresponding to that particular silicon content. 'Only inferior results are' obtained with preliminary thickness-reducing passes of about each (say reducing sheet metal from a thickness of 2 millimeters to 1 millimeter, and then againfrom 1 millimeter to 0.5 millimeter), and the results. secured with my improved process perior.

are far sufrom 0.7 to 0.5 millimeter.

should amount to from 20 to 5% in at least the last of the preliminary or main passes, and preferably in all of said passes.

In the case of 2% silicon sheet metal of initially 2 millimeters thickness and of a desired reduced thickness of 0.5 millimeter, I would for instance,

employ four stages or rolling operations, the first reducing the thickness-from 2 millimeters to 1.4 millimeters, the second from 1.4 to 1 millimeter, the third from 1 to 0.7 millimeter, and the fourth These figures indicate that each stage or pass reduces the thickness by about 30%. In some cases it may be suflicient to apply the 30% or 35% reduction to the last two preliminary passes only.

Between successive preliminary passes, the material is generally heated to a suitable temperature, preferably in the range of from 800 to 850 centigrade.

I'have found that after this heating which is to be performed after each of the preliminary or main passes the material should be plunged in water, in order to obtain particular valuable electrical and magnetic properties. The water should have a. temperature of about 0 centigrade. It is also possible to employ, instead of water, a cooling liquid which has a temperature of below 0 centigrade. Then I heat the material to a temperature between 500 to 800 centigrade. By this process I obtain a uniform distribution of carbon which is favourable for the conversion of the carbon into graphite.

After the last preliminary pass, I heat the material to a temperature above or close to the A: point. The temperature to be employed at this step depends on the silicon content of the ma terial, and lies in the range of from 900 to 1250 centigrade, according as the silicon content ranges from 0.5 to 5%. For instance, with a silicon content of 2%, the best temperature for this step would be say above 900 centigrade.

Then follows the critical thickness-reducing pass or stage which has been referred to above, and thereupon a critical heat treatment at a temperature ranging from about 800 to 1000 centigrade, for instance according to the following table:

Critical tom- Slhcon content pemmm Percent Centigrade 0. 5 About am" 1 850 -860 2 930 950 3 940 -950 4 and over 950 Generally speaking, if the silicon content ranges from 0.5 to 1.8%, the critical temperature will range from 850 to about 900 centigrade, and with a silicon content of from 1.8 to 5%, the critical temperature will range from about 900 to 980 centigrade.

For instance, in the case of 2% silicon sheet steel which by four preliminary passes of about 30% each as described above has been brought from a thickness of 2 millimeters to one of 0.5 millimeter, the critical thickness-reducing pass might be about 8%, reducing the thickness from 0.5 millimeter to 0.46 millimeter, and the recrystallizing heat treatment immediately following such critical pass might be performed at a temperature of 900 centigrade.

It will be noted that the temperature during the heat treatment immediately following the critical pass, is relatively high, and at least for the higher percentages of silicon indicated, lies above the temperature of 900 which hitherto was considered the upper liinit for this treatment stage, as it was found'hitherto that the watt-loss figures became quite unfavorable (too high) when this temperature was exceeded.

However, I have discovered that the detrimental effects (overheating or burning") heretofore observed could be eliminated, and exceedingly favorable results obtained, notwithstanding the use of temperatures of 900 and above in the recrystallizing heat treatment, if such treatment was followed by a heat treatment at a lower temperature, say from 700 to 850 centigra'de, lasting a considerable length of time, for instance ten hours. This additional heat treatment at a lower temperature increased the valuable properties of the material very materially. Thus the maximum permeability was more than doubled in certain cases. For instance, two materials which after a recrystallizing treatment performed at a temperature of 980, showed a maximum permeability of 2800 and 8000 respectively, had such maximum permeability increased to 6600 and 17,800 respectivelyby a supplemental heat treatment lasting ten hours at temperature of 800 centigrade. As the critical percentage of thick reduction is quite low in the case of high silicon content, for instance 0.5% of thickness reduction, it is difficult to roll the material with such a low degree of thickness reduction. Thus I have found that the material gets a certain internal stress by the critical thickness reduction and that I may obtain this certain internal stress by plunging the heated material (above 900 centigrade) into water of about 0 centigrade or into a cooling liquid of below 0 centigrade. After the plunging into water or into the cooling liquid the material should be heated to the critical temperature from about 900 to 1000" centigrade, as described above.

The improved results obtained by my process are clearly indicated by the very favorable figures which the product shows as to electrical characteristics, and particularly the low wattloss and'the high magnetic induction. Thus a silicon-alloyed steel with 0.03 C 0.12 M'n 2.00 Si 0.014% P 0.019% S treated according to my invention and reduced to sheets or strips of 0.5 millimeter thickness showed a loss of 1.8 watts per kilogram at a magnetic.induction of 10,000 gauss. A similar steel containing 3.3% of silicon and'about the above mentioned content of C, Mn, P and S, and reduced to a thickness of 0.35 millimeter showed a loss of 1.02 watts per kilogram at a magnetic induction of 10,000 gauss. Two steels of 0.4 millimeter thickness and containing 2.92 and 3.3% of silicon respectively, showed respective losses of 1.3 and 1.21 watts per kilogram at a magnetic induction of 10,000 gauss.

I claim:

1. Process for increasing the valuable electrical andmagnetic properties ot a steel containing from 0.5% to 5.0% of silicon, which comprises subjecting the steel to a plurality of preliminary cold rolling operations in each of which .cold rolling operations in each of which the thickness is reduced by from 20% to 35%, heatthe thickness is reduced by not more than about 35%, heating the steel intermediate between each of such rolling operations to a temperature of at least about, 800 C., heatingthe steel after the last preliminary operation to a temperature of at least 9001C, then cold rolling the steel and reducing its thickness'by an amount less, than in said preliminary rolling operations which is critical to the production'of crystal growth on subsequent annealing and which is between 0.5% and and then heating the steel to a, temperature above 800 C. v 2. Process for increasing the valuableelectrical and magnetic properties of} a steel contain- 15 ing from 0.5% to 5.0% of silicon, which comprises subjecting the steel to a plurality of preliminary cold rolling operations in each of which the thickness is reduced by from 5% to 35%, r heating the steel intermediate between each. of such rolling operations to a temperature of from 800 C. to 850 C. heating the steel after the last preliminary operation to atemperature of from 900 C. to 1250 C., then cold rolling the steel and reducing its thickness by an amount less than in said preliminary rolling operations which is critical to the production of crystal growth .on subsequent annealing and which lies between 0.5% and 15%, and then heating the steel to a temperature between 800 C. and 1000 C.

3. Process for increasing the valuable electrical and magnetic properties of a steel containing a from 0.5% to 3.5% of silicon, whichcomprises subjecting file steel to a plurality of preliminary ing the steel intermediate between each of such rolling operations to a temperature of from 800 C. to 850. C., heating the steel after the 'last pre- 5 liminary operation to a temperature of from 900 C. to 1250 C., thencold rolling the steel and reducing its thickness by an amount vless than in said preliminary rolling operations which is critical to the production of crystal growth on 10 subsequent annealing and which lies between i 1% and' 12%, and then heating the steel to a temperature between 850 C. and 950 C.

4. Process for increasing the valuable electrical and magnetic'properties of a steel cont in- 15 ing from 0.5% to 5.0% of silicon, which com prises subjecting the steel to a plurality of preliminary cold rolling operations in each of which the thickness is reduced by not more than about heating the steel intermediate between each 20 of such rolling operations to a temperature of at least about 700 C., heating the steel after the last preliminary operation to a temperature of at least floo" C.. then cold rolling thesteel and reducing its thickness. by anamount 25" less than in said preliminaryyrolling operations which is'critical to the production of crystal growth on subsequent annealing and between 0.5% and 15% then heating the steel to a temperature above 900 C., and then" heatiiig"the"'30-- steel to a temperature between 700 C. and 850 C.

ANTON WIMMER. 

